In recent years, the use of projection type display devices has become widespread, and in addition to their installation in conference rooms or the like for use in presentations and the like, they are increasingly installed for use in an environment where there are a lot of dust particles or the like such as stores, outdoors, etc. For projection type display devices installed in an environment where there are a lot of dust particles or the like, dust particles or the like sometimes adhere to the surface of the projection lens (i.e., the surface of a lens disposed at the front most part in a plurality of lenses of the projection lens). When dust particles or the like adhere to the surface of the projection lens, a reduction in brightness or variations in brightness occur in images projected by projection type display devices.
A cover is disposed on a projection lens to prevent dust particles or the like from adhering to the surface of the projection lens when projection type display devices are not used. However, when projection type display devices are installed in an environment where there are a lot of dust particles or the like, a lot of dust particles or the like adhere to the surface of the projection lens that is being used. Consequently, it is necessary for such projection type display devices to have a mechanism for cleaning the surface of the projection lens that is being used.
First, as a first lens cleaning mechanism, non-contact type lens cleaning mechanisms in which a cleaning unit is not directly contacted with a lens will be described.
For non-contact type lens cleaning mechanisms, for example, there is one mechanism in which a cleaning unit blows air to a lens surface and blows off and removes dust particles or the like adhering to the lens surface during the cleaning operation. In projection type display devices having a non-contact type lens cleaning mechanism, since the cleaning unit does not obstruct the surface of a projection lens even when a cleaning operation is performed during the projection of images, there is an advantage in that the cleaning operation does not affect the images to be projected.
JP2003-228127A describes a non-contact type lens cleaning mechanism in which a cleaning unit blows air to a lens surface during a cleaning operation. This lens cleaning mechanism comprises an air filter for removing dust particles or the like contained in the air, wherein the air filter is configured such that air that has passed through the air filter is blown to the lens surface. In this lens cleaning mechanism, this makes it possible to prevent dust particles or the like contained in the air from adhering to the lens surface during the cleaning operation.
However, in this lens cleaning mechanism, although large dust particles or the like adhering to the lens surface with a weak force such as static electricity can be removed, it is difficult to remove micro dust particles adhering to the lens surface or dust particles or the like containing moisture. Furthermore, it is particularly difficult to remove oily dust particles or the like.
As described above, since projection type display devices having a non-contact type lens cleaning mechanism have insufficient power to remove the dust particles or the like adhering to the surface of the projection lens, sometimes the occurrence of a reduction in brightness or variations in bright of the images to be projected cannot be sufficiently prevented.
Next, as a second cleaning mechanism, contact type lens cleaning mechanisms in which a cleaning unit is directly contacted with a lens will be described.
In contact type lens cleaning mechanisms, a cleaning unit having felt or the like is brought into direct contact with the lens surface to apply mechanical force to dust particles or the like adhering to the lens surface for removing the dust particles or the like. For this purpose, contact type lens cleaning mechanisms have a strong force to remove the dust particles or the like adhering to the lens surface, and can remove even micro dust particles, dust particles containing moisture, and oily dust particles or the like.
JP2006-220835A describes a contact type lens cleaning mechanism having a configuration similar to a windshield wiper that wipes away raindrops on the automobile windshield. This lens cleaning mechanism comprises a wiper, as a cleaning unit, that is a rod-shaped wiping structure, one end of which is rotatably supported by a lens frame that holds a lens.
In this lens cleaning mechanism, a drive system reciprocatingly moves the wiper along the lens surface in the state in which the wiper is pressed against the lens surface. Thus, the wiper wipes away dust particles or the like adhering to the lens surface.
However, in projection type display devices having this lens cleaning mechanism, when the cleaning operation is performed during use of the device, the wiper obstructs the lens surface to affect the images to be projected. Therefore, in such contact type lens cleaning mechanisms, it is sometimes necessary to reduce the area of the cleaning unit that obstructs the lens surface or to reduce the number of times and the period of time during which the cleaning unit obstructs the lens surface during the cleaning operation.
Furthermore, since the lens surface is a curved surface, it is necessary for this lens cleaning mechanism to deform the wiper in accordance with the shape of the lens surface when the wiper reciprocates along the lens surface in order to wipe the whole lens surface. For deforming the wiper in accordance with the shape of the lens surface, it is necessary to form the wiper in a complicated configuration. Providing this kind of lens cleaning mechanism results in expensive costs.
Moreover, in this lens cleaning mechanism, it is necessary to provide space adjacent to the lens frame which allows the wiper to be retracted during times other than the time when the cleaning operation is performed. Therefore, the size of devices that are provided with this lens cleaning mechanism increases.
In addition, since only one end of the wiper is supported by the lens frame, the pressing force of the wiper against the lens surface is strong in the portion on one end side of the wiper, which is supported by the lens frame, whereas the force is weak in the portion on the other end side, which is not supported by the lens frame. Therefore, in this lens cleaning mechanism, variations in wipes tend to occur on the lens surface. The occurrences of variations in wipes on the surface of the projection lens of projection type display devices cause variations in brightness of images to be projected.